You can also get the Downloads section of the Library through the 3 bar menu > Downloads. What do you mean by "The animation ... still works though"? Trying a new profile is a quick way of testing whether it's your profile or the software (presumably your distro's version).

https://support.mozilla.org/en-US/kb/troubleshoot-and-diagnose-firefox-problems https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems (also deals with hardware acceleration)

https://support.mozilla.org/en-US/kb/profile-manager-create-remove-switch-firefox-profiles https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data#w_what-information-is-stored-in-my-profile

What do you mean by "The animation ... still works though"?

The circular progress bar that replaces the button while files are downloading.

Trying a new profile is a quick way of testing whether it's your profile or the software (presumably your distro's version).

Dealing with multiple profiles is a mess. But the panel acts normal in a private window.

Something obviously broke. The question is what & why. There is nothing that should interfere with it.

I'll check the extensions later and see if any of them is doing wonky things.

Note that you can possibly open about:downloads via a bookmark.

Updating to version 100 has solved the issue.